Linear actuator with braking device

ABSTRACT

An actuator for connecting a reversible, rotary driving means to a load to be linearly moved and positioned thereby and employing a sleeve having a flange externally formed on one end portion thereof and having an external thread or the like on the opposite end portion. An internal thread or the like, directed oppositely to the external thread, is formed in the sleeve end portion having the external flange. The sleeve is coaxially positioned within and its external thread engaged with a generally cylindrical structure. A threaded shaft is coaxially positioned within and its thread engaged with the sleeve internal thread. Forces imposed on the sleeve and originating in torques imposed on the cylindrical structure or shaft urge the sleeve flange into braking contact with one or the other of a pair of annular members, each of which members is located at a respective side of the sleeve flange and is free to rotate only in a direction opposite to that in which the other of such members if free to rotate.

United States Patent [72] Inventor Roy A. Nelson Grand Prairie, Tex.[21] Appl. No. 66,423 [22] Filed Aug. 24, 1970 [45] Patented Dec. 28,1971 [73] Assignee LTV Aerospace Corporation Dallas, Tex.

[54] LINEAR ACTUATOR WITH BRAKING DEVICE 11 Claims, 8 Drawing Figs.

[52] US. Cl 192/8 R, 74/424.8 R [51] Int. Cl. B60t 7/14, Fl6h 1/ 16 [50]Field of Search 192/8,148; 74/424.8 R

[56] References Cited 1 UNITED STATES PATENTS 2,480,212 8/1949 Baines192/8 R UX 2,653,691 9/1953 Weiland 192/8 R 2,969,222 1/1961 Sears 192/8R X 192/8 R 74/424.8 R X 3,017,975 1/1962 Kinser 3,269,199 8/1966Deehanetal ABSTRACT: An actuator for connecting a reversible, rotarydriving means to a load to be linearly moved and positioned thereby andemploying a sleeve having a flange externally formed on one end portionthereof and having an external thread or the like on the opposite endportion. An internal thread or the like, directed oppositely to theexternal thread, is formed in the sleeve end portion having the externalflange. The sleeve is coaxially positioned within and its externalthread engaged with a generally cylindrical structure. A threaded shaftis coaxially positioned within and its thread engaged with the sleeveinternal thread. Forces imposed on the sleeve and originating in torquesimposed on the cylindrical structure or shaft urge the sleeve flangeinto braking contact with one or the other of a pair of annular members,each of which members is located at a respective side of the sleeveflange and is free to rotate only in a direction opposite to that inwhich the other ofsuch members if free to rotate.

PATENTEUnmemn 3,630,32

SHEET 1 or 3 ROY A. NELSON INVENTOR ATTORNEY PATENTED 05628 I97! SHEET 20F 3 N .Ek

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ROY A. NELSON INVENTOR BY 763 ATTORNEY PATENTEU 05:28:91: 3.630.328

SHEET 3 OF 3 ROY A. NELSON Fla 7 INVENTOR BY W ATTORNEY LINEAR ACTUATORWITH BRAKING DEVICE This invention relates to clutches and powerdelivery controls of an actuator, and more particularly to transmissioncontrol and automatic braking of a ball-screw actuator, which controland braking is responsive to imposed driving-means torque to releaseincorporated brakes.

A positioning system may utilize various combinations of mechanisms tocouple a rotary driving means to a load to be linearly moved andpositioned thereby relative to a fixed structure. One mechanism oftenemployed in such a positioning system is a braking and couplingmechanism. Such a mechanism is capable of acting not only as a directlydriving coupling when the rotary driving means is operative,.but is alsocapable of preventing torque-producing forces from the load to be movedand positioned from being transmitted back through the mechanism to therotary driving means, thus preventing either overspeeding of the rotarydriving means or overrunning of the desired load position, if thetorque-producing force is in the same direction as the torque beingproduced by the rotary driving means. A braking and coupling mechanismis further capable of acting as a brake, when the rotary driving meansis inoperative, to prevent torque-producing forces from the load frombeing transmitted through the mechanism to the idle rotary driving meansand concurrently to lock the load to be moved and positioned in a setposition.

A braking and coupling mechanism may be employed for direct coupling ofa rotary driving means to a load to be positioned; generally, however, abraking-coupling mechanism is used in cooperation with an actuator whicheffects a gear reduction of the rotary speed of the rotary driving meansand changes the rotary motion to linear motion. The mechanism,therefore, is generally located between the rotary driving means and anactuator.

A braking-coupling mechanism is not always utilized as a separate deviceand may be incorporated within an actuator. This has been frequentlydone, for example, in the aircraft industry where specially designedequipment is often made necessary because of critical weight and spacelimitations.

Most actuators incorporating a ball-screw device efficiently utilize, toposition a load, an input torque provided by a rotary driving means; forlittle of the input torque is needed to overcome frictional forcesbetween the balls and the screw. The driving means for ball-screwactuators, therefore, usually require one-third or less the powerrequired for driving means of other types of actuators. Ball-screwactuators are utilized throughout industry, but are exceptionallyattractive for actuation of control surfaces for airplanes because ofthe relatively smaller and, consequently, lighter-weight driving meansthat ball-screw actuators require.

A braking-coupling mechanism is especially desirable, if not essential,for use with or incorporation within a ball screw actuator, for thefriction in most ball screw actuators is so low that a load-imposedforce at the ball screw actuator output connection will tend to reverseor overspeed the ball screw actuator driving means.

Existing ball screw actuators which incorporate brakingcoupling deviceshave numerous shortcomings, especially in applications wheresynchronization of multiple positioning systems is essential and theloads impose torque-producing forces on the actuator output connectionsthat result in torques either in the same direction as the torque fromthe rotary driving means or in torques in the opposite direction.Existing ball screw actuators incorporating braking-coupling deviceshave further, undesirable characteristics in applications where weightand cost of the positioning systems are influencing factors, longoperating life of the actuators is necessary, andreliable lockup,release, and positioning of the load to be moved and positioned aremandatory.

Actuators of one existing type incorporate a brakingcoupling mechanismand work well enough when new but become unreliable with wear. Suchactuators usually have the common feature of components (such as leversand ball-ramp devices) that move to apply a force to a brake; but themovement of these components is limited, with the result that, when theymust move farther and farther to compensate for brake wear, theyeventually reach their limit of movement, and slippage then occurs.Without adjustment or replacement of parts, more and more slippageoccurs until little or no braking capability is left. Most existingbraking-coupling actuators have no convenient method of adjustment forwear to prolong their service life. Adjustment in many types of suchactuators entails partial disassembly for replacement of worn parts, theaddition of shims, or the obtaining of access to adjusting screws.

Still other types of actuators incorporating braking-coupling devicesrequire very close manufacturing tolerances which vastly increase theunit cost of each device and the probability of failure because ofcontamination typified by the introduction of metallic particles,generated from wear or during manufacturing, into clearances betweenmoving parts. An actuator, requiring close manufacturing tolerances andcontaining components made of dissimilar metals having differentcoefficients of expansion, is said to be temperature sensitive if anydifferential thennal expansion could cause possible seizing or gallingof components or could cause an increase in clearance that results inreduced braking power of the device. Temperature-sensitive actuatorshave, of course, restricted uses.

In other types of ball screw actuators incorporating brakingcouplingmechanisms, there are intentionally incorporated clearances betweenconnecting parts that result in looseness which makes difficult thesynchronization of multiple positioning systems and the precisepositioning of a load such as, for example, control surfaces of anairplane. Looseness" refers herein to a condition permitting relativemovement or play between two parts drivingly connected so that motion ofone part relative to the other can occur. Limited back-motion of thedriven member, therefore, can occur with respect to the driving memberunder some conditions. Looseness-producing clearances are necessary inmany existing braking-coupling actuators which use arms or levers eitherto move and expand brake shoes or to move other components into and outof contact with friction surfaces; still other actuators containintentionally provided gaps between the teeth of splines to delaymovement of one shaft while, for example, drivingly connectedslip-clutches can disengage brakes.

Still another type of braking-coupling actuator performs well whenprimarily subjected to opposing loads, but wears out rapidly underconditions resulting when an object to be moved by the actuator tends tobe moved by other forces (e.g., airloads) in the same direction as thatin which the actuator is attempting to move the object; such a load isusually referred to as an aiding load. Braking-coupling actuators thatwear out rapidly under aiding loads inherently incorporate componentswhich continually drag or rub rotating surfaces under an aiding-loadcondition. Some actuators require input torques from the rotary drivingmeans that are larger than the input torques actually required merelyfor moving the load. This is true for actuators having one brakecontinuously acting in one rotative direction and another brakecontinuously acting in the other rotative direction; hence, the inputtorque must override a brake to move and position the load. As soon asthe driving means is turned ofi and rendered inoperative, at least onebrake immediately locks the load in position. Still other actuatorsincorporate continuously slipping clutches which consume and waste inputtorque from the rotary driving means, thereby lowering the efficiency ofthe positioning system.

Some other types of braking-coupling actuators require specificlimitations, often necessarily maintained within close tolerances, onthe maximum and minimum braking capacities of their brakes. Brakingcapacity may be defined in terms of percentage of input torque (e.g.,200 percent of the input torque). Braking capacity is controlled bycoefficients of friction of the braking surfaces. Usually, then,particular brakingsurface materials are used that will have the propercoefficients of friction. Experience, however, has shown that actuatorsof this type are very unreliable because wear, temperature, andcontamination (introduction of foreign particles between brakingsurfaces) radically change or affect coefficients of friction. If acoefficient of friction becomes too low, the actuator employing such abraking-coupling device will not brake sufficiently to lock the load;and, if the coefficient of friction becomes too high, the release of theload is prevented, for the torque required to release the brake exceedsthe torque capacity of the driving means. Another type ofbraking-coupling actuator incorporates a spring which applies a force tobrake discs; but, should a load to be moved'and positioned transmit atorque-producing force to the actuator which exceeds the constantspring-force applied to the brake discs, the actuator will permit loadslippage. Great care must, therefore, be used in determining the maximumtorques the load to be moved and positioned will transmit to theactuator to assure the selection of a spring that will supply anadequate force.

Still another type of braking-coupling actuator is not capable of smallincremental adjustments of the position of the load. An actuator of thistype usually incorporates a continuously operating brake that must beoverpowered before positioning of the load can be effected.Alternatively, such an actuator utilizes a single, locking-spring clutchon its output connection, which clutch is unlocked by rotation of theinput connection in either rotative direction, with the consequence thata change in the direction of the feedback torque from the load, whilethe load is being moved, could prevent braking. Braking-couplingactuators of other types have no mechanical brake-releases; thus, oncethe load is locked, a momentary overpowering of the brake is necessaryto initiate the release. An actuator of this type may incorporate tworotatably mounted, annular braking components, one of which componentsis prevented from rotating in one direction and the other of which isprevented from rotating in the opposite direction. Rotation of the inputor output connection of a mechanism of this type will cause an internalmember of the mechanism to move and to come into contact with one of theannular braking components. Should contact be made with one of theannular braking components by the internal member while the internalmember is tending to rotate in the direction in which the annularbraking component cannot rotate, then braking and locking will occur. Inorder to break su'ch contact with the surface of the annular brakingcomponent, however, a momentarily overpowering torque is required toinitiate movement of the internal member.

Heretofore, some braking-coupling actuators could overcome some of theabove-mentioned problems, but always at the expense of retaining one ormore of the remaining shortcomings.

It is, accordingly, a major object of the present invention to provide anew and improved actuator incorporating a brakingcoupling mechanism forconnecting a reversible, rotary driving means to a load to be linearlymoved and positioned thereby relative to a fixed structure.

Another object of the present invention is to provide a braking-couplingactuator with braking and locking capabilities substantially unaffectedby wear, temperature, or contamination of braking surfaces of theactuator.

A further object is to provide, in such an actuator, a mechanicalbrake-releasing mechanism which eliminates the need of excessive torqueto override and release the brake for permitting movement of the load,and which mechanism permits movement of the load in small, accuratelycontrolled increments.

Yet another object is to provide a braking-coupling actuator havingmeans for convenient, external adjustment for wear of braking surfaces.

A still further object is to provide a braking-coupling actuator that isas durable, reliable, and smooth in operation when positioning a loadwhich acts in the aiding direction as it is when positioning a loadwhich acts in the opposing direction with respect to the torquedirection of the driving means.

Still another object is to provide a braking-coupling actuator not onlywithout intentionally provided looseness, but without any loosenesswhich is above the negligible and acceptable limits within whichsynchronization of multiple positioning systems and precise positioningof the load may be obtained.

An additional object is to provide such an actuator that is simple,compact, and free of the need of close manufacturing tolerances whichwould increase the unit cost of the actuator and increase theprobability of failure occasioned by contamination or wear.

Another object is to eliminate the need, in the brakingcoupling portionof an actuator, for closely controlled tolerances on coefficients offriction and maximum braking capacity, thereby obviating the problem ofseizure and unreleasable locking occasioned by galling or undesiredincrease in maximum braking capacity on the one hand, or of loss oflocking capability accompanying wear and a consequent reduction ofbraking capacity on the other.

A further object of this invention is to eliminate brake slippage in abraking-coupling actuator attributable to load-imposed forces.

A still further object is to provide such an actuator which does notexcessively consume and waste input torque.

Other objects and advantages will be evident from the specification andclaims and the accompanying drawing illustrative of the invention.

In the drawing:

FIGS. 1A and 1B are diagrammatic representations of a positioning systemincorporating the present invention;

FIG. 2 is a longitudinal, partially sectional view of the actuator ofthe present invention;

FIG. 3 is a partial, cross-sectional view taken along the line III-IIIin FIG. 2 and showing one end of the cylindrical structure threadopening into and connecting with the cylindrical structure first recess;

FIG. 4 is a partial, cross-sectional view taken along the line IV-IV inFIG. 2 and showing the opening into and connecting with the other end ofthe cylindrical structure thread in the cylindrical structure secondrecess;

FIG. 5 is a partial, cross-sectional view taken along the line V-V inFIG. 2 and showing one end of the sleeve internal thread opening intoand connecting with one end of the sleeve passageway;

FIG. 6 is a partial, cross-sectional view taken along the line VI-VI inFIG. 2 and showing the other end of the sleeve, which end opens into andconnects with the other end of the sleeve passageway; and

FIG. 7 is a partial, longitudinal, sectional view of a modification ofthe actuator of FIG. 2.

With reference to FIGS. 1A and 18, a diagrammatic representation of apositioning system utilizing a ball-screw actuator 10 havingincorporated therein a braking and coupling mechanism is shown inrespective plan and elevation views. A reversible, rotary driving means11 is connected to the actuator input connection 12, and a load 13(e.g., an airplane control surface) is connected to the actuatorball-screw output shaft 61. As long as the actuator output shaft 61 isrestrained from rotation about its axis, the actuator output shaft moveslinearly back and forth through and along the actuator axis 15 inresponse to torques imparted to the actuator input connection 12. Thepreferred method for preventing rotation of the actuator output shaft 61is to pivotally but nonrotatably connect it to a load 13 capable ofto-and-fro movement relative to and along the axis of the actuator 10,but incapable of rotation about the actuator axis 15. The actuator 10thus converts rotary motion to linear motion and moves and positions theload 13 between a first position 16 in which the load is shown in solidline and a second position shown at 16a in broken line. The actuator 10functions to convert torque from the rotary driving means 11 to linearmotion and transmit such linear motion to the load 13 when the drivingmeans is operative and, concurrently, prevents forces from the load frombeing transmitted back to the driving means. The rotary driving means11, therefore, cannot be overspeeded by forces from the load 13, nor canthe forces from the load prevent precise positioning of the load bycausing the driving means to overrun the desired load position. When therotary driving means 11 is inoperative, the actuator further acts as abrake which looks the load 13 in a set position and prevents forces fromthe load from being transmitted to the idle driving means.

In subsequent paragraphs, the direction of rotation of the actuatorinput connection 12 shall be determined by viewing its rotation from theinput connection side of the actuator 10, and the direction of rotationof the remainder of the actuator components shall be determined byviewing the rotation from the end of the actuator that is opposite tothe one where the output shaft 61 is connected to the load 13.

Referring now to FIG. 2, the actuator 10 comprises a housing 17preferably of a hollow, generally cylindrical shape having alongitudinal axis and provided on its exterior with two mutually spacedand hollow, cylindrical trunnions 18 which provide means for pivotalmounting of the housing on any desired fixed structure. The trunnions 18have axes that are coincident with each other and are perpendicular to aplane containing the housing axis 15. The housing 17 has first andsecond, open ends 19, 20 which are rigidly connected in a mutually fixedrelationship by a wall 21 defined by the intervening material betweenthe open ends of the housing and which open ends are transfixed by thehousing longitudinal axis 15 A first passageway 22 laterally penetratingthe housing wall 21 is provided through one of the trunnions l8, and,for added versatility, a similar passageway is provided through theother trunnion. For purposes of minimizing the housing weight, thehousing external diameter preferably is reduced between the trunnions 18and the housing second open end 19, thus forming an external groove 23.The housing 17 has an internal rim 24 at its first open end 19 and aninternal flange 25 having a face 26 perpendicular to the housing axis 15and facing toward the first open end 19. The flange 25 is locatedbetween the passageway 22 which laterally penetrates the housing and thehousing second, open end 20, but nearer the lateral penetrations thanthe second, open end. At the base and on the side confronting thelateral passageway 22, the housing internal flange 25 is provided with astep 27 on which rests a race of thrust bearing 29 (to be described). Aportion of the housing internal surface adjoining the step on whichrests one race of the thrust bearing 29 and extending from that step 27toward the lateral passageway 22 penetrating the housing underlies theother race of that same bearing in a manner allowing that other race toturn freely relative to the housing 17.

A generally cylindrical structure 32 has first and second open ends33,34, a second passageway 35 which is circular in cross section andextends through the cylindrical structure coaxially therewith, and alongitudinal axis 15 coincident with the housing axis. The internaldiameter of the cylindrical structure passageway 35 is larger in thatportion of the cylindrical structure 32 from the second open end 34 to apoint between the second recess 38 and the second, open end than is thediameter of the remaining portion of the cylindrical structurepassageway. The cylindrical structure 32 has a rounded-bottom, helicalthread 36 which is formed in the surface of the cylindrical structureforming the passageway 35. The thread 36 is of uniform depth throughoutits length. First and second elongated recesses 37, 38 are formed in thecylindrical structure internal surface; the first recess is locatedadjacent the cylindrical structure first, open end 33 and the secondrecess is located intermediate the cylindrical structure first andsecond, open ends 33, 34. As shown in FIGS. 3 and 4, each end of thecylindrical structure internal thread 36 opens into and terminates witha respective recess 37, 38. Each recess 37, 38 preferably has a diameterlarger than the diameter of the balls 62 (described later) which arelocated in the thread channels formed by the cylindrical structureinternal thread 36 and the external thread of the sleeve 49 (describedlater). The recesses 37, 38 provide extensions of the cylindricalstructure internal thread 36 to enable the balls 62. which substantiallyfill up the above-described thread channels, to roll along the threads36, 54. The recesses 37, 38 have means for urging the balls 62 from therecesses and into the threads 36, 54; such means being preferablyhelical springs 119.

The cylindrical structure 32 shown in FIG. 2 has first and secondexternally located flanges 39, 40 each having a face 41 or 42perpendicular to the cylindrical structure axis 15. The first-flangeface 41 faces toward the housing and the cylindrical structure firstopen ends 19, 33, and the second-flange face 42 faces toward the housingand cylindrical structure second open ends 20, 34. The cylindricalstructure 32 has an annular recess 43 between its first and secondexternal flanges 39, 40. The bottom of the annular recess 43 is ofuniform depth and thus forms a cylindrical, external surface which iscoaxial with the cylindrical structure axis 15. The width of the annularrecess 43 is smaller at its bottom than at its top, and the annularrecess sidewalls are therefore tapered. A set of gear teeth 44 is formedon the annular recess sidewall nearer the cylindrical structure secondexternal flange 40; the gear teeth thus encircle the cylindricalstructure axis 15. A means for drivingly connecting the cylindricalstructure 32 to the rotary driving means 11 is provided, said meanshaving extension through the housing first passageway 22 and being inthe form of a drive shaft 97 and gear (described later), which gearengages the cylindrical structure gear teeth 44.

The face of the second cylindrical structure flange 40, which face 42faces toward the cylindrical structure second open end 34, has providedtherein a step 45 which is spaced from the cylindrical structure bodyexternal surface and on which is mounted one race of a thrust bearing 29(to be described). On its face 41 which is the nearer to the cylindricalstructure first open end 33, the first cylindrical structure flange 39has a similar step 46 carrying a race of another thrust bearing 28 (tobe described).

An external shoulder 47 is formed on the cylindrical structure 32 at thejuncture of the exterior surface of the cylindrical structure and aportion of the cylindrical structure external surface which has areduced diameter; the reduced diameter portion of the cylindricalstructure exterior surface begins at the cylindrical structure secondopen end 34 and terminates at the cylindrical structure externalshoulder. The cylindrical structure external shoulder 47 has providedtherein a step 48 which is spaced from the reduced diameter portion ofthe cylindrical structure external surface and on which is mounted onerace of a thrust bearing 30 (to be described).

A sleeve-49 having a hollow, generally cylindrical shape, a longitudinalaxis 15, and first and second end portions 50, 51 is coaxiallypositioned within the housing 17 and cylindrical structure 32. Eachsleeve end portion 50 or 51 has a respective end face 52 or 53 which isperpendicular to the sleeve axis 15. The sleeve first end portion 50 hasa rounded-bottom, helical thread 54 which is formed on the externalsurface of the sleeve 49, which surface is symmetrically disposed aboutthe sleeve axis 15. The external sleeve thread 54 is of uniform depththroughout its length and matches the cylindrical structure thread 36 inshape, depth, width, and direction. The sleeve first end portionexternal diameter is smaller than the sleeve second end portion externaldiameter, and the sleeve first end portion internal diameter is largerthan the sleeve second end portion internal diameter. A portion of thesleeve first end portion 50 has a smaller external diameter than theexternal diameter of the remaining sleeve first end portion beginning atthe sleeve first end face 52 and terminating a relatively small distanceinwardly from the sleeve first end face. The sleeve second end portion51 has a thread 55 formed in-the inner, cylindrical surface of thesleeve 49, which surface is symmetrically disposed about the sleeve axis15. The sleeve second end portion internal thread 55 is similar to thesleeve first end portion external thread 54, but opposite in directionto the external thread of the first end portion 50. The sleeve secondend portion 51 has an external flange 56 formed or rigidly mounted onthe exterior thereof. The sleeve flange 56 has first and second,parallel faces 57, 58 which are perpendicular to the sleeve axis 15. Thesleeve second end portion 51 has a passageway 59 which connects the endsof the sleeve second end portion internal thread 55, thereby providing(in cooperation with the sleeve second end portion internal thread andthe thread 60 formed on the shaft 61, discussed later) a closed loop forcirculation of balls 62 (described later) within the sleeve second endportion internal thread. FIGS. and 6 show the respective ends of thesleeve internal thread 55 connect and terminate with the sleeve secondend portion passageway 59.

A cylindrical shaft 61 has a longitudinal axis 15 and extends coaxiallythrough the sleeve 49 and the housing 17. The shaft 61 has arounded-bottom, helical thread 60 which is formed in the surface of theshaft, which surface is symmetrically disposed about the shaft axis 15.The shaft thread 60 is of uniform depth throughout its length andmatches the sleeve internal thread 55 in shape, depth, width, anddirection. The means for drivingly connecting the shaft 61 to a load 13(not shown in FIG. 2) and for preventing the shaft from rotating aboutits axis 15 comprises a clevis 63 rigidly attached to one end of theshaft.

Uniformly sized balls 62 are placed within the thread-channelscooperatively formed by the cylindrical structure internal thread 36 andthe matching, in-register sleeve external thread 54 and the sleeveinternal thread 55 and the matching, in-register shaft thread 60. Thethread-channels are substantially filled with the balls 62, which ballsare sized to have a close rolling fit with the thread-channels anddrivingly connect the cylindrical structure 32 to the sleeve 49 and thesleeve to the shaft 61. The balls 62, therefore, enable the cylindricalstructure 32 and the shaft 61 to transmit and receive torqueproducingforces to and from the sleeve 49. The size of balls 62 filling thethread-channel formed by the cylindrical structure internal thread 36and the sleeve external thread 54, however, may be different from thesize of the balls filling the thread-channel formed by the sleeveinternal thread 55 and the shaft thread 60.

A first annular member 64 has first and second side faces 66, 67 thatare perpendicular to the first annular member and housing axes 15. A setof ratchet teeth 68 is formed in the circular outer surface of the firstannular member 64. The first annular member second side face 67confronts the sleeve external flange first face 57, and the firstannular member first end face 66 is provided with an outwardly extendingcircular step 69 located nearer the outer surface of the first annularmember 64, which surface contains the ratchet teeth 68, and on whichstep 69 rests a race of a thrust bearing 30 (to be described).

A second annular member 65 is substantially identical in construction tothe first annular member 64, except that the two members are mirrorimages of each other. The second annular member 65 thus has first andsecond side faces 70, 71, a set of ratchet teeth 72 formed on its outercircular surface, and a step 73 provided on its first face on whichrests a race of another thrust bearing 31 (to be described). The firstand second annular members second side faces 67, 7], consequently,mutually face each other; and each of them confronts a respective endface of the sleeve external flange 56.

The actuator is provided with means coaxially mounting the cylindricalstructure 32 and annular members 64, 65 within the housing 17 forrotation about the housing axis and preventing translation of thecylindrical structure and annular members relative to the housing, whichmeans will now be described. Employed in the above-mentioned means arefirst and second ball thrust bearings 28, 29 each having one racesurrounding and mounted on a respective cylindrical structure flangestep 45 or 46 and against a respective flange face 41 or 42. The outersurface of the remaining race of the first ball thrust bearing 28 restswithin and against the housing rim 24 and is held against outward motionrelative to the housing 17 by a first circular member 74 (describedlater). The

remaining race of the second ball thrust bearing 29 rests on the housinginternal flange step 27 and against the housing internal flange face 26.When thus mounted within the housing 17, the planes in which thesurfaces of the races of the first and second ball thrust bearings lieare perpendicular to the housing axis l5.

Employed in the means coaxially and rotatably mounting the annularmembers are third and fourth ball thrust bearings 30, 31. The third ballthrust bearing 30 has one race which surrounds and is mounted on thecylindrical structure external shoulder step. 48 and is positionedagainst the cylindrical structure external shoulder 47. The outersurface of the remaining race of the third ball thrust bearing 30 restsagainst the first annular member circular step 69 and is positionedagainst the first annular member first side face 66. The fourth ballthrust bearing 31 has one race positioned against the second annularmember first side face 70 and an outer surface which is snuglysurrounded by the second annular member circular step 73. The remainingrace of the fourth ball thrust bearing 31 is held against radial andoutwardly axial movement relative to the housing 17 by a second circularmember 75 (described later). When thus mounted within the housing 17,the planes in which the surfaces of the races of the third and fourthball-thrust bearings 30, 31 lie are perpendicular to the housing axis15.

First and second circular members 74, 75 each having a respective sideface 76 or 77 and a centrally located aperture 80 or 81 therethrough areeach coaxially with and removably attached to a respective housing openend 19 or 20 by fastening means such as respective pluralities of bolts78, and lock washers 79, 86. When the circular members 74, 75 areattached to the housing 17, the circular member side faces 76, 77 areperpendicular to the housing axis 15. The first circular member 74 hasan outer diameter approximately equal to the outer diameter of thehousing 17, and the diameter of the aperture 80 is larger diameter thanthe external diameter of the sleeve first endportion 50, with which itis in register. Where necessary, the first circular member 74 is locallythinned to provide clearance between that member and the cylindricalstructure first end 33. The face of the first circular member 76 facesinwardly with respect to the housing 17 and is thus in contact with boththe housing first open end 19 and, as above mentioned, a race of thefirst ball thrust bearing 28.

The second circular member 75 (without regard to its flange, to bedescribed) has an outer diameter slightly less than the internaldiameter of the housing 17. The diameter of the second circular memberaperture 81 is larger than the external diameter of the sleeve secondend portion 51, with which it is in register. The face of the secondcircular member 75 extends within the housing second open end 20 and hasa coaxial, circular recess 82 formed therein. The wall of the recess 82forms a circular step 83 which is intermediate the inner and outerdiameters of the second circular member. The race of the fourth ballthrust bearing 31 opposite to the one in contact with the second annularmember 65 rests against the second circular member recess step 83 andagainst a portion of the bottom of the second circular member recess 82between the step and the circular member aperture 81. The secondcircular member 75 has an outer flange 84 that has an outer diameterapproximately equal to the outer diameter of the housing 17. The secondcircular member 75 is attached to the housing 17 by the above-mentionedfastening means 85, 86. Material of the second circular member 75 ispreferably removed from its outer side for purposes of minimizing theweight of the actuator.

A means for applying a dragging force to the sleeve 49 for opposingrotary movement of the sleeve relative to the housing 17 comprises atleast one annular, resilient component 87 or 88 positioned around oneend of the sleeve and removably attached to the first or second circularmember 74 or 75. The preferred actuator of FIG. 2 has a first annular,resilient component 87 having an outer diameter larger than the diameterof the first circular member aperture 80 and an internal diametersmaller than the diameter of the reduced external diameter portion ofthe sleeve first end portion 50 adjacent the sleeve first end face 52.The first resilient component 87 is coaxial with and removably attachedto the side of the first circular member 74 that is opposite to the onecontaining the face 76 by a first thin, annular retainer 89 and screws90. The first resilient component 87 is thinned in the region of itsinternal diameter to increase its flexibility in this region and thusfacilitate the interference installation of the first resilientcomponent around the reduced-diameter portion of the sleeve first endportion 50. Although not essential, the actuator of FIG. 2 also has asecond annular, resilient component 88 having an outer diameter largerthan the diameter of the second circular member aperture 81 and aninternal diameter smaller than the external diameter of the sleevesecond end portion 51. The second resilient component 88 is coaxial withand removably attached to the side of the second circular member 75 thatis opposite to the one containing the face 77 by a second thin, annularretainer 91 and screws 92. As in the case of the first resilientcomponent 87 and for the same reason, the thickness of the secondresilient component 88 is thinned at its internal diameter. Besidesproviding a dragging force to the sleeve 49, the resilient components87, 88 also serve as dust or lubricant seals to prevent the entry offoreign matter into the actuator 10 or to retain a lubricant. lt will beunderstood that the means for applying a dragging force to the sleeve 49for opposing rotary movement of the sleeve relative to the housing 17may comprise any suitable structure slidingly connected between thesleeve and the housing.

A means for preventing a first rotative movement of the first annularmember 64 in the counterclockwise direction and a means for preventing asecond rotative clockwise direction of movement of the second annularmember 65 with respect to the housing axis are preferably provided inthe form of two pair of ratchets 93, 94. A first and second pair ofpawls 95, 96 are mounted on the interior of the housing 17 at locationsin which each pawl is adjacent and confronts a respective set of annularmember ratchet teeth 68, 72. Each pawl of the pair of pawls 95, 96 ismounted 180 degrees apart and engaged with the ratchet teeth of itsassociated annular member 64, 65 to prevent counterclockwise movement ofthe first annular member and clockwise movement of the second annularmember.

The thread directions (i.e., right-hand or left-hand) of the cylindricalstructure internal thread 36 and corresponding sleeve external thread 54and the sleeve internal thread 55 and corresponding shaft thread 60 aredependent on the desired locking directions of the annular membersratchets 93, 94. The embodiment in H6. 2 necessarily depicts aright-hand thread for the sleeve internal thread 55 and a right-handthread for the shaft external thread 60 to correspond with the lockingagainst counterclockwise direction of movement by the first annularmember ratchets 93.

A means for drivingly connecting the cylindrical structure 32 to therotary driving means 11 (refer to FIG. 1A) comprises a drive shaft 97which has first and second ends 98, 99 and that is rotatably mountedwithin the housing first passageway 22, the shaft 97 having a gear 100rigidly mounted on its first end. The gear 100 is in engagement with theset of gear teeth 44 formed in the cylindrical structure, and the driveshaft second end 99 is provided with means for drivingly connecting itto the rotary driving means 11, said means for drivingly connectingbeing a square male fitting 101.

The manner of rotatably mounting the drive shaft 97 preferably employs atubular member 102 having an internal flange 103 on one end and anexternal flange 104 on the other end. When the tubular member 102 ispositioned, internal flange end first, within the housing firstpassageway 22, the outside diameter of the tubular member has a closesliding fit with the inner surface of the housing first passageway. Theouter diameter of the tubular member external flange 104 isapproximately equal to the outer diameter of the trunnion 18. Theportion of the drive shaft between its second end 99 and a pointintermediate the drive shaft first and second ends 98 and 99 has areduced diameter, and a shoulder 105 is thus formed at the juncture ofthese two portions of the drive shaft 97. A roller bearing 106 has aninner race 107 that surrounds and is mounted on the drive shaft 97 at alocation intermediate the rigidly attached gear and the drive shaftshoulder and an outer race 108 that rests against the tubular memberinternal flange 103 and the internal surface of the tubular member 102.A ball thrust bearing 109 has an inner race 110 that surrounds and ismounted on the portion of the drive shaft 97 having the reduced diameterand which is positioned against the drive shaft shoulder 105. The ballthrust bearing outer race 111 has a close, sliding fit with the innersurface of the tubular member 102. Y

A first annular spacer 112 is positioned between and in contact with theroller and ball thrust bearing outer races 108, 1 11.

A second annular spacer 113 having an external flange 114 on one end anda close sliding fit with the internal diameter of the tubular member 102is positioned within the tubular member with its flange resting on thetubular member flange 104. The end of the second annular spacer 113opposite to the one with the flange 114 rests against the outer race ofthe ball thrust bearing 109. The tubular member and second annularspacer external flanges 104, 114 are removably attached to the trunnionby a plurality of bolts 115 and lockwashers 116.

The reduced diameter portion of the drive shaft has an externallythreaded portion 117 on which a nut 118 is positioned. The nut 118 istightened against the inner race of the ball thrust bearing 109 to clampthe race 110 between the nut and the drive shaft shoulder 105.

In operation, the axial position of the second circular member 75 (FIG.2) is adjusted by the second circular member bolts 85 to bring thesecond annular member into relatively light dragging contact with thesleeve flange second face 58. Adjustment of the contacting force betweenthe second annular member 65 and the sleeve flange 56 can be readilyeffected by tightening or loosening the second circular member bolts 85.

With added reference to FIGS. 1A and 1B, the actuator 10 of theforegoing construction and arrangement has several functional modes, inall of which modes the housing 17 is pivotally mounted on any suitable,fixed structure by means of the trunnions 18. The first functional modeof the actuator 10 is one in which the driving means 11 is in thepower-off condition and a load-produced force is received by the shaft61, which force tends to move the shaft toward its retracted position,wherein the clevis 63 is near the housing first open end 19. The forcethus imposed on the shaft 61 by the load 13 is transmitted from theshaft to the sleeve 49 through the interconnecting plurality of balls 62located within the shaft and corresponding internal sleeve threads 60,55. As the shaft 61 is prevented from rotation relative to the actuator10 by its connection at the clevis 63 to a load, a wedging action of theballs 62 converts the axial force being transmitted to the sleeve 49from the shaft into force components: namely, an axial-thrust force anda rotational force. The thrust force acts in a direction that moves thesleeve flange 56 into firm contact with the second annular member 65and, concurrently, the rotational force acts in a direction which tendsto rotate the sleeve 49 in the clockwise direction. The clockwiserotational force thus imposed on the sleeve 49 rotates the sleeve arelatively small angular distance in the clockwise direction (e.g.,approximately 1 degree) before the sleeve is moved into firm contactwith the second annular member 65. The second annular member 65 islimited to rotation in the counterclockwise direction by its associatedratchets 94; thus, the second annular member prevents clockwise rotationof the sleeve 49 promptly upon the sleeve being strained against it bythe axial thrust force. During the incipient rotation of the sleeve 49and while transmitting the load-produced force from the shaft 61 to thesleeve, the balls 62 roll, for a relatively short distance (e.g.,approximately 0.02 inch), along the thread-channels formed by the shaftand sleeve internal threads 60, 55 and through the sleeve passageway 59which connects the ends of the sleeve internal thread. As soon as thesleeve 49 is braked and locked, the balls 62 stop rolling along thethread-channels. Before forces are transmitted from the sleeve 49 to thecylindrical structure 32 by the interconnecting plurality of balls 62located within the sleeve external thread and cylindrical structureinternal thread 54, 36, the second annular member 65 brakes and locksthe sleeve relative to the housing 17. In this functional mode,therefore, the actuator not only restricts a load 13 which imposes aforce on the shaft 6! to a negligible movement, but also prevents theload from being transmitted back to the idle driving means H which isconnected to the actuator drive shaft second end 99 that forms the inputmember connection 12.

The second functional mode to be discussed is one in which the drivingmeans 11 is in the power-off condition and the above-mentioned load 13is reversed and tends to move the shaft 61 to its extended position,wherein its clevis 63 is most widely spaced from the housing first openend 19. In this mode, as in the first functional mode, the load-producedforce is transmitted from the shaft 61 to the sleeve 49 through theballs 62 which are located within the thread-channels formed by theshaft thread 60 and sleeve internal thread 55. While transmitting theload-produced force to the sleeve 49, the wedging action of the balls 62converts this force into a thrust and a rotational force. The thrustforce in this functional mode acts in a direction that tends to unlockthe sleeve flange 56 from the second annular member 65 by relieving thestrain of the sleeve flange against the second annular member and movesthe sleeve flange away from the second annular member and into firmcontact with the first annular member 64. Concurrently, the rotationalforce received by the sleeve 49 tends to rotate the sleeve in thecounterclockwise direction and thus to move the flange away from thesecond annular member 65 and toward the first annular member 64. Beforecoming into finn contact with the first annular member 64, the sleeve 49rotates relative to the housing axis 15 a relatively small angulardistance in the counterclockwise direction. The first annular member 64,however, is limited to rotation in the clockwise direction by itsassociated ratchets 93; thus, the first annular member preventscounterclockwise rotation of the sleeve 49 when the sleeve is strainedagainst it by the axial thrust force. During this small rotationalmovement of the sleeve 49 (as in every rotational movement by thesleeve) the balls 62 roll along the thread-channels formed by the shaftand internal sleeve threads 60, 55 and circulate through the sleevepassageway 59 which connects the ends of the sleeve internal thread. Thedirection in which the balls 62 roll within and the length of movementby the balls along the thread-channels and sleeve passageway 59 dependon the angular movement of the sleeve 49 with respect to the housingaxis 15. Just as in the first functional mode, the first annular member64 and as sociated ratchets 93 brake and lock the sleeve relative to thehousing 17 before any force can be transmitted from the sleeve to thecylindrical structure 32 by the interconnecting plurality of balls 62located within the sleeve external thread 54 and cylindrical structureinternal thread 36.

The larger the load-imposed force while operating in this functionalmode, the larger the axial thrust force which forces the sleeve flange56 against the first annular member 64; thus, the actuator 10 eliminatesbrake slippage attributable to loadimposed forces, whether such forcesare large or suddenly applied. Elimination of brake slippageattributable to load-im- A third functional mode is one in which thedriving means 11 is initially in the power-off condition and there isimposed on the shaft 61 a load-produced force which tends to move theshaft to its retracted position and in which the driving meanssubsequently is selectively activated to the power-on andcounterclockwise output torque condition wherein a counterclockwisetorque is applied to the drive shaft of the actuator 10 forrepositioning the load 13 through movement of the shaft in the retract"or aiding direction. By an aiding load or a load acting in the aidingdirection" it is meant that the object to be moved by the actuator 10tends to be moved by other forces (e.g., airloads) in the same directionas that in which the actuator and driving means 11 is attempting to moveit. An opposing load," of course, is one in which the object to be movedby the actuator 10 tends to be moved by other forces in an oppositedirection to that in which the actuator and driving means 11 areattempting to move it. During the repositioning of the load 13 thatoccurs during operation in the third functional mode, the direction ofthe load-imposed force may be temporarily reversed to act in the extend"or opposing direction. Before the desired position of the load 13 isreached, the direction of the load-imposed force on the shaft 61 may bereturned to the retract" direction. The following description of thethird functional mode, therefore, depicts a repositioning of a load 13that initially acts in the aiding direction, changes to an opposingdirection, and changes back to the aiding direction; whereupon, afterthe desired load position is reached, the driving means 11 isdeactivated to its power-off condition, and the functional mode revertsfrom the third functional mode back to the first functional mode whereinthe load is locked, relative to the actuator housing 17 in a preciseposition.

To effect this repositioning of the load IS, the torque pro vided by thedriving means 11 rotates the drive shaft 97 and the drive shaft gear inthe counterclockwise direction. The drive shaft gear 100 is meshed withthe set of gear teeth 44 formed on the cylindrical structure 32 and thusdrives the cylindrical structure in the clockwise direction. Thecylindrical structure 32 transmits the driving-means torque it receivesto the sleeve 49 through the plurality of interconnecting balls 62located in thread-channels formed by the cylindrical structure internalthread 36 and the corresponding sleeve external thread 54. The sleeve 49in turn transmits the driving-means torque to the shaft 61 through theplurality of balls 62 located with the sleeve internal thread 55 andcorresponding shaft thread 60, and the shaft 61 responds by linearlymoving and retracting through the actuator 10 and thus repositioning theload 13.

Prior to activating the driving means 11, the actuator 10 functions in amanner similar to its operation during the first functional mode (i.e.,the load-produced force components received by the sleeve 49 act axiallytoward the second annular member 65 and rotationally in the clockwisedirection). As in the first functional mode, the sleeve 49 is forcedagainst the second annular member 65, and the sleeve and second annularmember are locked together against further relative rotational movementwith respect to each other. The sleeve 49 tends to rotate in theclockwise direction, but is locked against rotational movement relativeto the housing 17 by the second annular member 65 in cooperation withits clockwise, rotation-preventing ratchets 94. The actuator 10,therefore, locks the load 13 against movement relative to the actuator.

To effect repositioning of the load 13 in this functional mode, thedriving means H is activated to the power-on and counterclockwise torqueoutput condition. The counterclockwise torque thus imposed on the driveshaft 97 and drive shaft gear 100 by the driving means 11 drives thecylindrical structure 32 in the clockwise direction. The cylindricalstructure 32 transmits the clockwise torque to the sleeve 49 through theinterconnecting bails 62 located in the threadchannel formed by thecylindrical structure internal thread 36 and the sleeve external thread54.

The lightly dragging contact of each of the annular, resilientcomponents 87, 88 against the sleeve 49, however, produces a force onthe sleeve that opposes the incipient rotation of the sleeve, therebytending to cause momentary, relative rotation between the sleeve and thecylindrical structure 32. This relative rotation between the sleeve 49and cylindrical structure 32 immediately initiates a wedging actionbetween the balls 62 and the sides of the thread channels at both theshaft and cylindrical structure, thus substantially eliminating internalslippage within the actuator and, consequently, promoting precisepositioning of the load 13. The wedging action of the balls 62 convertsthe torque being transmitted to the sleeve 49 from the cylindricalstructure 32 into torque-equivalent force components which are similarto the force components generated by the wedging action of the ballslocated in the shaft and sleeve internal threads 60, 55 described in thefirst and second functional modes: namely, an axial thrust-force and arotational force.

While transmitting the torque to the sleeve 49, the balls 62 move (aswill be described) along channels formed by the cylindrical structureinternal thread 36 and sleeve external thread 54 for a relatively shortdistance (e.g., approximately 0.02 inch) in a direction towardcylindrical structure second recess 38. Each cylindrical structurerecess 37 or 38 has a means for urging the balls 62 from the recesses;the embodiment shown in FIGS. 2, 3, and 4 utilize compressed helicalsprings 119 for such ball-urging means. Movement of the balls 62 in thisfunctional mode thus results in additional compression of the helicalspring 119 contained in the second cylindrical structure recess 38 andlessens the compression of the other helical spring contained in thefirst cylindrical structure recess 37. Such ball movement is required topermit the balls 62 to roll rather than skid in the thread-channels, andthus to protect the thread-channels from excessive wear. The amount ofball movement is directly related to the amount of relative movementbetween the cylindrical structure 32 and the sleeve 49, and suchrelative movement between the cylindrical structure and sleeve isdependent upon the axial travel of the sleeve relative to the housing17, which axial movement is limited to the clearance between the annularmembers 64, 65 and respective sleeve flange faces 57, 58. The movementof the sleeve 49 relative to the cylindrical structure 32 and movementof the balls 62 along the thread-channels formed by the cylindricalstructure and sleeve external threads 36, 54 are both relatively small.

The axial thrust force received by the sleeve 49 from the cylindricalstructure 32 acts in a direction which moves the sleeve flange 56 awayfrom the second annular member 65 and toward the first annular member64, thus relieving the strain of the sleeve flange against the secondannular member, which strain against the second annular member wascaused by the load-imposed force. The rotational force componentsreceived by the sleeve 49 from the driving means 11 and the load 13 bothact in the clockwise direction. If the loadproduced forces received bythe sleeve 49 are relatively large, the force components received by thesleeve from the driving means 11 reduce the force holding the sleeveagainst the second annular member 65 enough to permit slippage betweenthe sleeve flange 56 and second annular member. If large enough, theoutside forces acting on the load 13 (e.g., wind forces on an airplanecontrol surface) actually reposition the load with the driving means 11simply releasing the brakes of the braking-coupling actuator 10. Duringthis repositioning of a relatively large aiding load, the sleeve flangesecond face 58 continually slips against the second annular member 65;and, since the cylindrical structure 32 and sleeve 49 are lockedtogether by their interconnecting balls 62, the cylindrical structureand sleeve rotate together about their common axis 15. When the sleeve49 rotates, it transmits a net rotational force which acts in theclockwise direction to the shaft 61 through the interconnecting balls 62located in the thread channels formed by the sleeve internal thread 55and the shaft thread 60. The wedging action of the balls 62 converts theclockwise rotational force transmitted to the shaft 61 into an axialthrust-force which acts in the retract" direction and a rotational forcewhich is neutralized by the means which prevents rotation of the shaftrelative to the housing axis 15 (as will be described). The shaft 61thus retracts linearly through and outwardly from the housing secondopen end 20.

In the preferred embodiment depicted in FIGS. 1A, 1B, and 2, the meansfor preventing the shaft 61 from rotating comprises a clevis 63 rigidlyattached to one end of the shaft, which clevis is pivotally butnonrotatably connected to a load 13 capable of to-and-fro motionrelative to and along the axis of the actuator 10, but incapable ofrotation about the actuator axis 15. A number of alternate ways ofpreventing rotation of the shaft 61 about its own axis 15 may, ofcourse, be effectively utilized in lieu of a connection to a load 13incapable of rotation about the actuator axis; as for example, a pinmounted through the shaft end opposite to the end connected to the load,which pin rides in a groove or elongated slot formed in a componentfixedly mounted on structure that is fixed relative to the pivotalmountings of the actuator 10 (example not shown).

If the load-produced force received by the sleeve 49 is relativelysmall, the force components of the torque received by the sleeve fromthe driving means 11 overcome the loadproduced force holding the sleeveagainst the second annular member 65, and the net axial force acts inthe direction of the first annular 64; the sleeve flange 56 thus movesfrom contact with the second annular member and into contact with thefirst annular member. The first annular member 64 is free to rotate inthe clockwise direction, and the first annular member, sleeve 49, andcylindrical structure 32 therefore rotate as an assembly and in thatdirection, thereby driving the shaft 61, as explained above, in theretract direction.

When the load-imposed force received by the shaft 61 changes from actingin the retract direction to the extend direction, the load-imposed forcecomponent received by the sleeve 49 from the shaft also changesdirection. The axial thrust-force from the load 13 acts in the directionwhich tends to move the sleeve 49 toward the first annular member 64,and the rotational force from the load acts in the counterclockwisedirection. The net axial thrust force received by the sleeve 49 acts tomove the sleeve toward the first annular member 64 and thus moves thesleeve flange 56 away from the second annular member 65 and into firmcontact with the first annular member 64. As the driving-means torque isalways greater than an opposite, load-produced torque, the netrotational force component received by the sleeve 49 acts in theclockwise direction. The sleeve 49 thus continues to transmit aclockwise rotational force to the shaft 61 through the interconnectingballs 62. The actuator 10, therefore, smoothly and efficiently continuesthe repositioning of the load 13 in the retract" direction, during whichtime the ratchets 93 allow free rotation of the first annular member 64.

Before the desired position of the load 13 is reached and in the exampledescribed, the direction of the load-imposed force returns to theoriginal retract direction. The net forces received by the sleeve 49return it from contact with the first annular member 64 to slight,dragging contact with the second annular member 65. Since both the loadand the driving-means rotational force components act in the clockwisedirection, the net rotational force received by the sleeve 49 continuesto be in the clockwise direction. The sleeve 49 thus continues totransmit a clockwise rotational force to the shaft 61 through theinterconnecting balls 62. The shaft 61 which is restrained from rotationabout its axis 15, continues to move the load 13 smoothly in the retractdirection.

When the desired position of the load 13 is reached and upon the drivingmeans 11 being deactivated to place it in its power-off condition, thetorque applied by the driving means to the cylindrical structure 32through the drive shaft 97 and gear 100 is eliminated. The forcesreceived by the sleeve 49 are substantially the same as described in thefirst functional mode, and the load 13 is precisely locked in a setposition.

The third functional mode illustrates that the actuator is as durable,reliable, and smooth in operation when positioning an aiding load aswhen positioning an opposing load; for, although slippage may occurbetween the sleeve flange 56 and one of the annular members 64 or 65,the contact between the sleeve flange and respective annular member isrelatively light, and the contacting surface areas are relatively large.The pressure of the sleeve flange 56 against a respective annular member64 or 65, when slippage occurs during the repositioning of an aidingload, is relatively low; thus, no galling or rapid wear occurs.Moreover, such light contact between the relatively large contactingsurface areas of the sleeve flange 56 against a respective annularmember 64 or 65 prevents a large temperature increase in the rubbingparts.

A fourth functional mode is one in which the driving means 11 isinitially in the power-off condition, the load-imposed force on theshaft 6] acts in the retract" direction, and the driving meanssubsequently is selectively activated to the power-on and clockwiseoutput torque condition to reposition the load 13 by moving the shaft inthe extend direction. This is an opposing-load condition, since theload-imposed force tends to retract the load 13 and the driving means 11attempts to extend the load. Prior to activating the driving means 11,the actuator 10 is in the same condition as described in the firstfunctional mode. After activation of the driving means ll in the fourthfunctional mode, the cylindrical structure 32 is driven by the driveshaft 97 and drive shaft gear 100 in the counterclockwise direction. Thedriving-means torque received by the cylindrical structure 32 istransmitted to the sleeve 49 in a manner similar to that which occurs inthe third functional mode, except that the balls 62 located in thethread-channels formed by the cylindrical structure and sleeve externalthread 36, 54 roll a relatively short distance in a direction toward thecylindrical structure first recess 37 and the driving-means torquecomponents received by the sleeve act in opposite directions relative tothose in the third functional mode. In this fourth functional mode, theaxial thrust force component received by the sleeve 49 from the drivingmeans 11 acts in a direction toward the second annular member 65, thusadding to the axial thrust force produced by the load 13 anduninterruptingly continuing the strain of the sleeve flange 56 againstthe second annular member; as a consequence, the sleeve and secondannular member remain locked together against rotational movementsrelative to each other. Simultaneously with the above, a rotationalforce component of the torque received by the sleeve 49 from the drivingmeans 11 tends to rotate the sleeve in the counterclockwise direction, adirection opposite to the direction that the load 13 tends to rotate thesleeve. Since the counterclockwise rotational force component of thetorque received by the sleeve 49 from the driving means 11 is largerthan the clockwise rotational force component received by the sleevefrom the load 13, the net rotational force imposed on the sleeve acts inthe counterclockwise direction; therefore, the sleeve departs from atendency to rotate in the clockwise direction and tends to rotate in thecounterclockwise direction. The second annular member 65 is free torotate in the counterclockwise direction, for its associated ratchet 94prevents only clockwise rotation; therefore, the mutually locked sleeveflange 56 and second annular member are free to rotate with thecylindrical structure 32 in the counterclockwise direction. Concurrentlywith the above, the sleeve 49 transmits the net rotational forcecomponent, as a counterclockwise torque, to the shaft 61 through theinterconnecting balls 62 located in the sleeve internal thread 55 andthe shaft thread 60. The wedging action of the balls 62 located in thethread-channels formed by the sleeve internal thread 55 and shaft thread60 converts the counterclockwise torque transmitted by the sleeve 49 tothe shaft 61 into a rotational force which acts in the counterclockwisedirection and an axial thrust force which acts in the extend" direction.The shaft 61, as described before, moves linearly, under the influenceof the axial thrust force, in the extend" direction.

When the desired position of the load 13 is reached and upon the drivingmeans 11 being deactivated to place it in its power-off condition, thetorque applied by the driving means to the cylindrical structure 32through the drive shaft 97 and gear 100 is eliminated. The cylindricalstructure 32, thus having ceased to be driven by the driving means 11 inthe counterclockwise direction, has only a load-produced force on it,which force immediately tends to reverse the counterclockwise rotationof the sleeve 49.

When the driving means 11 is deactivated, therefore, the axial thrustand rotational forces received by the sleeve 49 are substantially thesame as described in the first functional mode (i.e., the axial thrustforce acts in the direction towards the second annular member 65 and therotational force acts in the clockwise direction). Since the axialthrust force acts in the same direction, whether the driving means 11 isin the poweron or power-off condition, the sleeve 49 remainsuninterruptedly locked to the second annular member 65. The clockwise,load-produced force received by the sleeve 49 tends to rotate the sleevein the clockwise direction, but such rotation is immediately braked andlocked, relative to the housing 17 and with substantially no possibilityof motion of the sleeve relative to the housing, by the second annularmember 65 and its associated clockwise rotation opposing ratchet 94.When the sleeve 49 is thus locked, the shaft 61 and the load 13connected thereto are also similarly locked. Because the actuator iscapable of the operations described above in connection with its thirdand fourth functional modes, intentionally provided looseness (necessaryin many existing braking-coupling actuators) is not required in thepresent actuator 10; and the actuator, because of the absence of suchlooseness, is thus capable of providing precise positioning of the load13. Furthermore, the braking-coupling actuator 10, without requiringclose manufacturing tolerances, is devoid of any looseness of connectionwhich is above the negligible and acceptable limits within whichsynchronization of multiple positioning systems is obtainable.

A fifth functional mode is one in which the driving means 11 isinitially in the power-off condition, the load-imposed force on theshaft 61 acts in the extend direction, and the driving meanssubsequently is selectively activated to the power-on andcounterclockwise output torque condition to reposition the load 13 bymoving the shaft in the retract direction. This functional mode involvesan opposing-load condition, since the load-imposed force tends to extendthe shaft 61 and the driving means 11 attempts to retract the load.Prior to activating the driving means 11, the actuator 10 is in the samecondition as described in the second functional mode. After activationof the driving means 11 in this functional mode, the cylindricalstructure 32 is driven, by the drive shaft 97 and drive shaft gear 100,in the clockwise direction. The driving-means torque received by thecylindrical structure 32 is transmitted to the sleeve 49 in a mannersimilar to that in the third and fourth functional modes. In this fifthfunctional mode, the axial thrust force component received by the sleeve49 from the driving means 11 acts in a direction tending to move thesleeve toward the first annular member 64 and thus adds to the axialthrust force produced by the load 13 and uninterruptingly continues thestrain of the sleeve flange 56 against the first annular member; as aconsequence, the sleeve and second annular member remain locked togetheragainst rotational movement relative to each other. Concurrently withthe above, a rotational force component of the torque received by thesleeve 49 from the driving means 11 tends to rotate the sleeve in theclockwise direction, a direction opposite to the direction that the load13 tends to rotate the sleeve. Since the clockwise rotational forcecomponent of the torque received by the sleeve 49 from the driving means11 is larger than the counterclockwise rotational force componentreceived by the sleeve from the load 13, the net rotational forceimposed on the sleeve acts in the clockwise direction; therefore, thesleeve departs from a tendency to rotate in the counterclockwisedirection and tends to rotate in the clockwise direction. The

first annular member 64 is free to rotate in the clockwise direction,for its associated ratchet 93 prevents only counterclockwise rotation;therefore, the mutually locked sleeve flange 56 and first annular memberare free to rotate, with the cylindrical structure 32, in the clockwisedirection. During the above, the sleeve 49 transmits the net rotationalforce component, as a clockwise torque, to the shaft 61 through theinterconnecting balls 62 located in the sleeve internal thread 55 andthe shaft thread 60. The wedging action of the balls 62 located in thethread-channels formed by the sleeve internal thread 55 and shaft thread60 converts the clockwise torque transmitted by the sleeve 49 to theshaft 61 into a rotational force and an axial thrust force. The means 63for preventing the shaft 61 from rotating about its axis neutralizes therotational force received by the shaft; but the axial thrust forcereceived by shaft, which acts in the retract" direction, moves the shaftand load 13 in the retract" direction of the shaft.

When the desired position of the load 13 is reached and upon the drivingmeans 11 being deactivated to place it in its power-off condition, thetorque applied by the driving means to the sleeve 49 through thecylindrical structure 32, the drive shaft 97, and gear 100 iseliminated. The sleeve 49, thus having ceased to be driven by thedriving means 11 in the clockwise direction, has only a load-producedforce imposed on it, and the load-produced force immediately tends toreverse the clockwise rotation of the sleeve, which tendency isprevented by means described below.

When the driving means 11 is deactivated, therefore, the axial thrustand rotational forces received by the sleeve 49 are substantially thesame as described in the second functional mode (i.e., the axial thrustforce acts in the direction tending to move the sleeve flange 56 towardthe first annular member 64 and the rotational force acts in thecounterclockwise direction). Since the axial thrust force acts in thesame direction, whether the driving means 11 is in the power-on orpower-off condition, the sleeve 49 remains uninterruptedly locked to thefirst annular member 64. The counterclockwise, load-produced forcereceived by the sleeve 49 tends to rotate the sleeve in thecounterclockwise direction, but such rotation is immediately braked andlocked, relative to the housing 17 and with substantially no possibilityof motion of the sleeve relative to the housing, by the first annularmember 64 and its associated, counterclockwiserotation opposing ratchet93. When the sleeve 49 is thus locked, the shaft 61 and the load 13connected thereto are also similarly locked.

If, before reaching the desired position of the load 13, theload-imposed force on the shaft 61 reverses and acts in the retractdirection, then the load-imposed force components received by the sleeve49 act in opposite directions; namely, a thrust force component whichtends to move the sleeve flange 56 toward the second annular member 65and a rotational force component which tends to move the sleeve in theclockwise direction. The axial thrust force component of theload-imposed force thus opposes the axial thrust force componentreceived by the sleeve 49 from the driving means 11, and the rotationalforce component of the load-imposed force acts in the same direction asthat of the rotational force component received by the sleeve from thedriving means.

The net axial thrust force received by the sleeve 49 continues to act ina direction toward the first annular member 64, but decreases inmagnitude after the change in direction of the load-imposed force. Thus,the sleeve 49 initially remains uninterruptedly locked to the firstannular member 64. When the direction of the net axial thrust forcecomponent changes, as is the case when the net rotational forcecomponent received by the sleeve 49 is greater than the rotational forcecomponent of the driving means torque received by the sleeve, the netaxial thrust force unlocks the sleeve from the first annular member 64by relaxing the strain of the sleeve from the first annular member andmoves the sleeve away from contact with the first annular member andinto contact with the second annular member 65. Since the second annularmember 65 is prevented from clockwise rotation by its associated ratchet94, braking of the sleeve occurs as soon as the clockwise-rotatingsleeve 49 contacts the second annular member. Consequently, the load 13cannot overspeed the driving means 11 when acting in the aidingdirection relative to the torque-direction of the driving means;moreover, an aiding load cannot prevent precise positioning of suchload, for as soon as the desired position is reached and upon thedriving means being placed in its power-off condition, the torqueapplied to the sleeve 49 by the driving means is eliminated and thebraking-coupling actuator 10 immediately reverts to its first functionalmode of operation. Once the actuator 10 is in the first functional modeof operation, the load 13 is immediately locked, relative to the housing17 and with substantially no possibility of movement of the sleeve 49relative to the housing, as described in connection with the firstfunctional mode. The sleeve responds substantially immediately to forcesreceived by it from the driving means. Thus, the sleeve locks or unlocksrelative to the housing substantially immediately in response toactivation or deactivation of the driving means. Consequently, theactuator 10 permits movement of the load 13 in small, accuratelycontrolled increments by manual or automatic activation and deactivationof the driving means 11.

Unlike the existing braking-coupling actuators, the actuator 10described herein contains a mechanical brake-releasing mechanism of aconstruction which eliminates the need of excessive torque to overrideor to disengage brakes in order to position a load. it is important tonote that the brake-releasing mechanism of the present actuator 10utilizes force components to disengage and shift the sleeve 49 from theannular member 64 or 65 that brakes and locks the load 13 relative tothe housing 17, with the aid of an associated ratchet 93 or 94, to theannular member that has an associated ratchet that permits rotation inthe rotative direction of the driving means torque and thus permits thedriving means 11 to reposition the load. The operations which occur inthe fifth functional mode further illustrate that such an actuator 10 isas durable, reliable, and smooth in operation when positioning a loadwhich acts in the aiding direction relative to the torque direction ofthe driving means 11 as it is when positioning a load which acts in theopposing direction relative to the torque direction of the drivingmeans.

The sixth and last functional mode is one in which the driving means 11is initially in the power-off condition, the load imposed force on theshaft 6] acts in the extend direction, and the driving meanssubsequently is selectively activated to the power-on and clockwiseoutput torque condition to reposition the load 13 by moving the shaftload in the extend direction. This mode involves an aiding loadcondition, since both the load-imposed force and the driving means 11tend to extend the load. Prior to activating the driving means 11, theactuator 10 is in the same condition as described in connection with thesecond functional mode. After activation of the driving means 11 in thesixth functional mode, the cylindrical structure 32 is driven by thedrive shaft 97 and drive shaft gear 100 in the counterclockwisedirection. The driving means torque received by the cylindricalstructure 32 is transmitted to the sleeve 49 through the plurality ofinterconnecting balls 62 located in the cylindrical structure and sleeveexternal threads 36, 54 in a manner similar to that in the otherfunctional modes. The axial thrust force component received by thesleeve 49 from the driving means 11 acts in a direction toward thesecond annular member 65, thus opposing the axial thrust force imposedon the sleeve by the load 13. During the above, a rotational forcecomponent of the torque received by the sleeve 49 from the driving means11 tends to rotate the sleeve in the counterclockwise direction, whichis the same rotative direction that the load 13 tends to rotate thesleeve.

The axial thrust force received by the sleeve 49 from the driving means11 through the cylindrical structure 32 acts in a direction which tendsto move the sleeve flange 56 away from the first annular member 64 andtoward the second annular member 65, thus relieving the strain of thesleeve flange against the first annular member. The rotational forcecomponents received by the sleeve 49 from the driving means 11 and theload 13 both act in the counterclockwise direction. If the load-producedforces received by the sleeve 49 are relatively large, the net axialthrust force component received by the sleeve from the load 13 anddriving means 11 reduces the force holding the sleeve flange 56 againstthe first annular member 64 enough to permit slippage between the sleeveflange and first annular member. As in the third functional mode, thedriving means 11 merely releases the brakes of the braking-couplingactuator and the outside forces acting on the load actually repositionthe load 13. During this repositioning effected by a relatively largeaiding load, the sleeve flange first face 57 continually slips againstthe first annular member 64; and, since the cylindrical structure 32 andsleeve 49 are locked together at their interconnecting balls 62, thecylindrical structure and sleeve rotate together about their common axis15. When the sleeve 49 rotates, it transmits a rotational force (whichacts in the counterclockwise direction) to the shaft 61 through theinterconnecting balls 62 located in the thread-channels formed by thesleeve internal thread 55 and the shaft thread 60. The wedging action ofthe balls 62 converts the counterclockwise rotational force transmittedto the shaft 61 into an axial thrust force which acts in the extend"direction and a rotational force which is neutralized by the means 63which prevents rotation of the shaft relative to the housing axis 15.The shaft 61 thus moves, in its extend direction, linearly through andoutwardly from the housing first open end 19.

If the load-produced force received by the sleeve 49 is relativelysmall, the force components of the torque received by the sleeve fromthe driving means 11 overcomes the loadproduced force holding the sleeveflange 56 against the first annular member 64 and the net axial forceacts in the direction tending to move the sleeve flange toward thesecond annular member 65; the sleeve flange thus moves from contact withthe first annular member and into contact with the second annularmember. The second annular member 65 is free to rotate in thecounterclockwise direction, and the second annular member, sleeve 49,and cylindrical structure 32 thus rotate as an assembly, thereby drivingthe shaft 61 and load 13, as explained above, linearly and in the extenddirection of the shaft.

When the desired position of the load 13 is reached and upon the drivingmeans 11 being deactivated to place it in its power-off condition, thetorque applied by the driving means to the sleeve 49 through thecylindrical structure 32, the drive shaft 97, and gear 100 iseliminated. The sleeve 49, thus having ceased to be driven by thedriving means 11 in the counterclockwise direction, has only aload-produced force imposed on it, and the load-produced forceimmediately tends to reverse the counterclockwise rotation of the sleeveand is prevented from doing so as will appear below.

When the driving means 11 is deactivated, therefore, the axial thrustand rotational forces received by the sleeve 49 are substantially thesame as described in the second functional mode (i.e., the axial thrustforce acts in the direction tending to move the sleeve toward the firstannular member 64, and the rotational force acts in the counterclockwisedirection) and the load 13 is precisely locked in a set position.

The braking-coupling actuators capability of braking and locking a loadis substantially unaffected by wear of the contacting surfaces of theactuators sleeve flange 56 and the annular members 64, 65 because therelative axial movements between the sleeve flange and annular membersare not limited to a specific maximum dimension. If wear increases theclearance between the sleeve flange 56 and an annular member 64, or 65,and sleeve 49 is capable of increased axial movement with respect tosuch annular member, and the sleeve flange is thus always capable ofbeing promptly moved into firm contact with one of the annular members.The only adverse affect of wear on such an actuator 10 is in theintroduction of a relatively small amount of looseness between thesleeve flange 56 and the annular members 64, 65 which is caused by anincrease in clearance between the sleeve flange and annular members.Part of the undesired relative axial movement between the sleeve flange56 and the annular member 64, 65 can be eliminated by tightening thesecond circular member bolts 85, which tightening of the bolts 85 movesthe second circular member 75, forth ball thrust bearing 31, and thesecond annular member 65 inwardly with respect to the housing second end20 and thus reduces the clearance between the sleeve second flange face58 and the second annular member. The bolts 85, which are locatedoutside the housing 17, therefore present a means for convenient,external adjustment for wear.

Since firm contact is always obtainable between the sleeve flange 56 andannular member 64, 65 the braking surfaces of the sleeve flange andannular members do not require closely controlled tolerances to obtain areliable braking and locking capability for the braking-couplingactuator 10. Further, a maximum braking capacity, above which capacityslippage occurs, is not employed; for, unlike many existingbrakingcoupling actuators and by virtue of employment of a mechanicalbrake-releasing mechanism, the driving means torque does not have tooverride brakes to reposition a load. Inherent problems associated withclosely controlled tolerances of coefficients of friction, such asseizure and unreliable locking occasioned by wear-induced galling on onehand or loss of locking capability accompanying wear and a consequentreduction of braking capacity on the other, are eliminated because ofsuch tolerances are not utilized in the actuator 10.

The braking-coupling actuator 10 described herein is simple, compact,and free of the need of close manufacturing tolerances that are requiredof many existing braking-coupling actuators; therefore, not only is theunit cost of such an actuator lowered, but its construction reduces theprobability of failure because of wear-generated contamination (i.e.,the introduction of wear-generated, metallic particles into clearancesbetween moving parts). Moreover, the lower tolerances and largerclearances between parts utilizable in the actuator of the presentinvention minimize the effects of large temperature changes on thevarious components.

Although the resilient components 87,88 are in continuous, draggingcontact with the sleeve 49, such contact is relatively light and theenergy or torque received by the sleeve from the driving means 11 thatis thus consumed by the frictionproduced force of the resilientcomponent is so small as to be negligible. The actuator of FIG. 2,therefore, does not excessively consume and waste input torque.

A modification of the present invention as depicted in H6. 7, is one inwhich the second circular member 75 of FIG. 2 is replaced by aring-shaped member 120, the sleeve flange 56 is provided with aplurality of holes 121, and a plurality of bolts 122 removably fastenthe ring-shaped member to the cylindrical structure second end 34through the sleeve flange holes. The ring-shaped member has an outerdiameter preferably approximately equal to outer diameter of thecylindrical structure 32 and an internal diameter that is approximatelyequal to the internal diameter of that portion of the cylindricalstructure adjacent its second open end 34. A portion of the exteriorsurface of the ring-shaped member 120 has a reduced diameter, and thejuncture of the two external diameters forms a shoulder 124. The face ofthe shoulder of the ring-shaped member 120 is perpendicular to thehousing axis 15 when the ring-shaped member is attached to thecylindrical structure 32 by the bolts 122. The shoulder 124 has providedthereon and at its base a circular step 126 which is spaced from thereduced diameter portion of the external surface of the ring-shapedmember 120 on on which is mounted the race of the fourth ball thrustbearing 31 opposite the one in contact with the second annular member65. The circular step 126 is formed by removing as much material of theringshaped member 120 as necessary to permit clearance of the race ofthe fourth ball thrust bearing 31 that is in contact with the secondannular member 65 and is perpendicular to the shoulder 124. Thering-shaped member shoulder 124 is in contact with the race of thefourth ball thrust bearing 31 that rests on the ring-shaped membercircular step 126.

The axial position of the ring-shaped 120 is adjusted by the bolts 122to bring the second annular member 65 into relatively light draggingcontact with the sleeve flange second face 58. As before described,clearance between the second annular member 65 and sleeve flange 56 isreadily effected by tightening or loosening the ring-shaped member bolts122. If desired, an annular dust or lubricant seal (not shown) could beprovided and mounted in a manner similar to the mounting of the secondcircular member 75 as shown in FIG. 2.

In operation, the braking-coupling actuator of FIG. 7 functions insubstantially the same manner as the above-described actuator of FIG 2.Rotational movement of the ring-shaped member 120 and the cylindricalstructure 32 relative to the sleeve 49 is relatively small, and thesleeve flange holes 121 are sized larger than the ring-shaped memberbolts 122 passing through them to permit such relative rotationalmovement.

What is claimed is:

1. An actuator for connecting a reversible, rotary driving means to aload to be linearly moved and positioned thereby relative to a fixedstructure, said actuator comprising:

a housing having first and second open ends, a longitudinal axistransfixing the ends, a wall rigidly connecting the ends in a fixedrelation to each other, a first passageway laterally penetrating thewall, and means for pivotally mounting the housing on said fixedstructure;

a generally cylindrical structure having first and second open ends, alongitudinal axis coincident with the housing axis, a second passagewayextending through the cylindrical structural and coaxial therewith, andan internal thread, the cylindrical structure being provided with meansfor drivingly connecting it to the rotary driving means, said means fordrivingly connecting having extension through the housing firstpassageway;

a cylindrical sleeve coaxial with the housing and having a longitudinalaxis and first and second end portions each provided with a thread, thesleeve first end portion thread being external and matching thecylindrical structure internal thread and the sleeve second end portionbeing internal and of a direction opposite to the direction of thesleeve first end portion thread, the sleeve second end portion having aflange rigidly mounted on the exterior thereof, said flange having firstand second, parallel faces which are perpendicular to the sleeve axis,and each of the sleeve end portions having an end face;

a cylindrical shaft extending through a coaxial with the sleeve andhaving a longitudinal axis and a thread matching the sleeve second endportion internal thread, the shaft being provided with means fordrivingly connecting it to a load and for preventing the shaft fromrotating about its axis;

a plurality of balls mounted within all the above-mentioned threads andin connecting relation between the shaft and sleeve and between thesleeve and the cylindrical structure;

first and second annular members each having a side face confronting arespective one of the sleeve flange faces;

means coaxially mounting the cylindrical structure and annular memberswithin the housing for rotation about the housing longitudinal axis andpreventing translation of the cylindrical structure and annular membersrelative to the housing; and

means preventing rotation of one of the annular members in a firstdirection and of the other annular member in a second direction aboutthe housing axis.

2. The actuator claimed in claim 1, said means for preventing rotationof one of the annular members in a first direction and of the otherannular member in a second direction about the housing axis comprising apair of ratchets.

3. The actuator of claim 1, there being provided within the sleevesecond end portion a passageway which connects the ends of the sleeveinternal thread, thereby providing, in cooperation with the sleeveinternal thread and shaft thread, a closed loop for continuouscirculation of the balls within the sleeve internal thread; and

first and second recesses provided in the cylindrical structure, thefirst recess being provided at one end of the cylindrical structureinternal thread and the second recess provided at the other end of thecylindrical structure thread, each recess having a diameter larger thanthe diameter of the balls, the recesses providing extensions of thecylindrical structure and external sleeve threads to enable the balls toroll along the threads.

4. The actuator of claim 3, each of said threads being substantiallyfilled with ones of said balls and said cylindrical structure recesseshaving means for urging balls from the recesses and into the cylindricalstructure threads.

5. The actuator of claim 1, said means coaxially mounting thecylindrical structure and annular members within the housing forrotation about the housing longitudinal axis and preventing translationof the cylindrical structure and annular members relative to the housingcomprising:

an internal flange on the housing and having a face perpendicular to thehousing axis and facing toward the housing first open end;

a shoulder externally located on the cylindrical structure and having aface which faces toward the housing second open end;

first and second flanges externally located on the cylindrical structureand each having a face perpendicular to the cylindrical structure axis,the first-flange face facing toward the housing first open end and thesecond-flange face facing toward the housing second open end;

first and second circular members each having a face and a centrallylocated aperture therethrough, each of the circular members beingremovably attached to a respective housing open end and being positionedwith its face facing inward with respect to the housing; and

a plurality of thrust bearings, one of the thrust bearings beingpositioned between and in contact with the housing internal flange faceand the cylindrical structure secondflange face, anotherof the thrustbearings being positioned between and in contact with the cylindricalstructure first-flange face and the face of the circular member attachedto the housing first open end, another of the thrust bearings beingpostiioned between and in contact with the first annular member and theface of the cylindrical structure shoulder, and yet another of thethrust bearings being positioned between and in contact with the secondannular member and the face of the circular member attached to thehousing second open end.

6. The actuator of claim 5, said actuator being provided with means forapplying a dragging force to the sleeve for opposing rotary movement ofthe sleeve relative to the housing.

7. The actuator of claim 6, said means for providing a dragging force tothe sleeve comprising at least one annular resilient componentpositioned around one end of the sleeve and removably attached to atleast one of the circular membets.

8. The actuator of claim 1, said sleeve flange having a plurality ofholes and said means coaxially mounting the cylindrical structure andannular members within the housing for rotation about the housinglongitudinal axis and preventing translation of the cylindricalstructure and annular members relative to the housing comprising:

an internal flange on the housing and having a face perpendicular to thehousing axis and facing toward the housing first open end;

a shoulder externally located on the cylindrical structure and having aface which faces toward the housing second open end;

first and second flanges externally located on the cylindrical structureand each having a face perpendicular to the cylindrical structure axis,the first-flange face facing toward the housing first open end and thesecond-flange face facing toward the housing second open end;

a circular member having a face and a centrally located aperturetheretrhough, the circular member being removably attached to thehousing first open end and positioned with its face facing inwardly withrespect to the housing;

a ring-shaped member removably attached to the cylindrical structure bya plurality of bolts passing through the sleeve flange holes and havinga face facing the cylindrical structure second end; and

a plurality of thrust bearings, one of the bearing being positionedbetween and in contact with the housing internal flange face and thecylindrical structure second-flange face, another of the thrust bearingsbeing positioned between and in contact with the cylindrical structurefirst-flange face and the circular member face, another of the thrustbearings being positioned between and in contact, with the first annularmember and the face of the cylindrical structure shoulder, and yetanother of the thrust bearings being positioned between and in contactwith the second annular member and the face of the ringshaped member.

9. The actuator of claim 1, said means for drivingly connecting thecylindrical structure to the rotary driving means comprising:

a set of gear teeth formed in the cylindrical structure and encirclingthe cylindrical structure axis;

a drive shaft having first and second ends and rotatably mounted withinthe housing first passageway, the drive shaft second end being providedwith means for drivingly connecting it to a rotary driving means; and

a gear rigidly mounted on the drive shaft first end and in engagementwith the gear teeth of the cylindrical structure.

10. The actuator of claim 1, the means for pivotally mounting thehousing comprising two coaxial, mutually spaced trunnions on theexterior of the housing, said trunnions having axes mutuallyperpendicular to a plane containing the housing axis.

11. The actuator of claim 10, the trunnion axes being coincident witheach other, the first passageway laterally penetrating the housing wallbeing provided through one of said trunnions, a similar passageway beingprovided through the other trunnion.

1. An actuator for connecting a reversible, rotary driving means to aload to be linearly moved and positioned thereby relative to a fixedstructure, said actuator comprising: a housing having first and secondopen ends, a longitudinal axis transfixing the ends, a wall rigidlyconnecting the ends in a fixed relation to each other, a firstpassageway laterally penetrating the wall, and means for pivotallymounting the housing on said fixed structure; a generally cylindricalstructure having first and second open ends, a longitudinal axiscoincident with the housing axis, a second passageway extending throughthe cylindrical structural and coaxial therewith, and an internalthread, the cylindrical structure being provided with means fordrivingly connecting it to the rotary driving means, said means fordrivingly connecting having extension through the housing firstpassageway; a cylindrical sleeve coaxial with the housing and having alongitudinal axis and first and second end portions each provided with athread, the sleeve first end portion thread being external and matchingthe cylindrical structure internal thread and the sleeve second endportion being internal and of a direction opposite to the direction ofthe sleeve first end portion thread, the sleeve second end portionhaving a flange rigidly mounted on the exterior thereof, said flangehaving first and second, parallel faces which are perpendicular to thesleeve axis, and each of the sleeve end portions having an end face; acylindrical shaft extending through a coaxial with the sleeve and havinga longitudinal axis and a thread matching the sleeve second end portioninternal thread, the shaft being provided with means for drivinglyconnecting it to a load and for preventing the shaft from rotating aboutits axis; a plurality of balls mounted within all the above-mentionedthreads and in connecting relation between the shaft and sleeve andbetween the sleeve and the cylindrical structure; first and secondannular members each having a side face confronting a respective one ofthe sleeve flange faces; means coaxially mounting the cylindricalstructure and annular members within the housing for rotation about thehousing longitudinal axis and preventing translation of the cylindricalstructure and annular members relative to the housing; and meanspreventing rotation of one of the annular members in a first directionand of the other annular member in a second direction about the housingaxis.
 2. The actuator claimed in claim 1, said means for preventingrotation of one of the annular members in a first direction and of theother annular member in a second direction about the housing axiscomprising a pair of ratchets.
 3. The actuator of claim 1, there beingprovided within the sleeve second end portion a passageway whichconnects the ends of the sleeve internal thread, thereby providing, incooperation with the sleeve internal thread and Shaft thread, a closedloop for continuous circulation of the balls within the sleeve internalthread; and first and second recesses provided in the cylindricalstructure, the first recess being provided at one end of the cylindricalstructure internal thread and the second recess provided at the otherend of the cylindrical structure thread, each recess having a diameterlarger than the diameter of the balls, the recesses providing extensionsof the cylindrical structure and external sleeve threads to enable theballs to roll along the threads.
 4. The actuator of claim 3, each ofsaid threads being substantially filled with ones of said balls and saidcylindrical structure recesses having means for urging balls from therecesses and into the cylindrical structure threads.
 5. The actuator ofclaim 1, said means coaxially mounting the cylindrical structure andannular members within the housing for rotation about the housinglongitudinal axis and preventing translation of the cylindricalstructure and annular members relative to the housing comprising: aninternal flange on the housing and having a face perpendicular to thehousing axis and facing toward the housing first open end; a shoulderexternally located on the cylindrical structure and having a face whichfaces toward the housing second open end; first and second flangesexternally located on the cylindrical structure and each having a faceperpendicular to the cylindrical structure axis, the first-flange facefacing toward the housing first open end and the second-flange facefacing toward the housing second open end; first and second circularmembers each having a face and a centrally located aperturetherethrough, each of the circular members being removably attached to arespective housing open end and being positioned with its face facinginward with respect to the housing; and a plurality of thrust bearings,one of the thrust bearings being positioned between and in contact withthe housing internal flange face and the cylindrical structuresecond-flange face, another of the thrust bearings being positionedbetween and in contact with the cylindrical structure first-flange faceand the face of the circular member attached to the housing first openend, another of the thrust bearings being positioned between and incontact with the first annular member and the face of the cylindricalstructure shoulder, and yet another of the thrust bearings beingpositioned between and in contact with the second annular member and theface of the circular member attached to the housing second open end. 6.The actuator of claim 5, said actuator being provided with means forapplying a dragging force to the sleeve for opposing rotary movement ofthe sleeve relative to the housing.
 7. The actuator of claim 6, saidmeans for providing a dragging force to the sleeve comprising at leastone annular resilient component positioned around one end of the sleeveand removably attached to at least one of the circular members.
 8. Theactuator of claim 1, said sleeve flange having a plurality of holes andsaid means coaxially mounting the cylindrical structure and annularmembers within the housing for rotation about the housing longitudinalaxis and preventing translation of the cylindrical structure and annularmembers relative to the housing comprising: an internal flange on thehousing and having a face perpendicular to the housing axis and facingtoward the housing first open end; a shoulder externally located on thecylindrical structure and having a face which faces toward the housingsecond open end; first and second flanges externally located on thecylindrical structure and each having a face perpendicular to thecylindrical structure axis, the first-flange face facing toward thehousing first open end and the second-flange face facing toward thehousing second open end; a circular member having a face and a centrallylocated aperture therethrough, the circular member being rEmovablyattached to the housing first open end and positioned with its facefacing inwardly with respect to the housing; a ring-shaped memberremovably attached to the cylindrical structure by a plurality of boltspassing through the sleeve flange holes and having a face facing thecylindrical structure second end; and a plurality of thrust bearings,one of the bearing being positioned between and in contact with thehousing internal flange face and the cylindrical structure second-flangeface, another of the thrust bearings being positioned between and incontact with the cylindrical structure first-flange face and thecircular member face, another of the thrust bearings being positionedbetween and in contact with the first annular member and the face of thecylindrical structure shoulder, and yet another of the thrust bearingsbeing positioned between and in contact with the second annular memberand the face of the ring-shaped member.
 9. The actuator of claim 1, saidmeans for drivingly connecting the cylindrical structure to the rotarydriving means comprising: a set of gear teeth formed in the cylindricalstructure and encircling the cylindrical structure axis; a drive shafthaving first and second ends and rotatably mounted within the housingfirst passageway, the drive shaft second end being provided with meansfor drivingly connecting it to a rotary driving means; and a gearrigidly mounted on the drive shaft first end and in engagement with thegear teeth of the cylindrical structure.
 10. The actuator of claim 1,the means for pivotally mounting the housing comprising two coaxial,mutually spaced trunnions on the exterior of the housing, said trunnionshaving axes mutually perpendicular to a plane containing the housingaxis.
 11. The actuator of claim 10, the trunnion axes being coincidentwith each other, the first passageway laterally penetrating the housingwall being provided through one of said trunnions, a similar passagewaybeing provided through the other trunnion.